Device for radiation therapy

ABSTRACT

Device, related to the means for radiation therapy of malignant and benign neoplasms and certain other diseases, comprise hollow probe  5,  source  1  of neutral particle radiation in the form of X-ray or gamma quanta or neutrons, and means of shaping the particle beam of said radiation oriented by the longitudinal axis of the probe. Means of shaping the particle beam is executed in the form of collimator or lens  18  comprising aggregate of curved channels for radiation transmission with a total internal reflection. Said means may be located inside of the probe  5.    
     On using the device, probe  5  is introduced into the body of patient  11,  with its distal end  7  approaching pathological locus  13  or inserted directly into it.  
     For exposure of pathological locus, use is made of radiation of the neutral particles source directly or secondary radiation excited in the target placed in the distal end of the probe or radiation dissipated with this target.  
     Design of the device requires no evacuation of the probe and use of high voltage in the latter, is easily transformed by the probe replacement, in particular, to change its size, to change energy and directional pattern of radiation affecting the pathological locus. Making of the probe removable simplifies its sterilization.  
     1 independent claim and 42 dependent claims, 10 figures of drawings.

Field of the Invention

[0001] The present invention relates to means for radiation therapy ofmalignant and benign neoplasms and certain other diseases.

Background of the Invention

[0002] At present, treatment with ionizing radiation is widely used notonly in the therapy of malignant neoplasms, but benign tumors and aseries of inflammatory and other diseases of nonneoplastic nature aswell (Aspects of Clinical Dosimetry, Ed. R. V.Stavitskij, Moscow,“MNPI”, 2000 [1] (in Russian)).

[0003] Devices are known for radiation therapy which comprise X-raysource, oriented for the purpose of directing radiation created with itto the pathological locus area. In order to minimize irradiation ofhealthy tissues surrounding pathological locus, such devices maycomprise several X-ray sources. The irradiation created with them isdirected to the pathological locus area from different directions(Radiation Therapy of Malignant Tumors. Guide for Physicians. Ed. Prof.E. S.Kiseleva, Moscow, “Meditsina” Publishing House, 1996 [2] (inRussian)).

[0004] Device is also known for radiation therapy comprising severalX-ray sources whose radiation, being aimed to the area of pathologicallocus from different directions, is focused with X-ray lenses(international application PCT/RU 00/00273, WO 01/29845A16 Apr. 26, 2001[3]). Due to the said focusing, radiation from each of the lenses onpassing through the healthy tissues has in them lower concentration thanin the pathological locus.

[0005] More radical way to decrease irradiation of healthy tissuessurrounding the pathological locus comprise its irradiation not fromoutside, but from the inside.

[0006] Such a way is realized, in particular, by implantation of acapsule with radioactive material directly into the pathological locus[2]. This method has drawbacks of the necessity of surgical interventionand associated with it difficulty in the control of irradiationduration.

[0007] The most close to the device proposed is a known device disclosedin U.S. Pat. No. 5,153,900 [4] (Russian analogue patent No. 2,155,413)and in number of other patents belonging to Photoelectron Corporation.This known device comprise a probe device for introduction directly intothe pathological locus or for approaching it. Probe device in saiddevice is a part of X-ray tube. Its anode is situated at the distal endof probe device. Proximal end of probe device adjoins the outlet ofmeans for electronic beam formation, which is directed along thelongitudinal axis of the probe device towards anode.

[0008] Within the probe of this device vacuum should be maintained (aswithin any X-ray tube). This fact in combination with the necessity ofhigh voltage supply to the anode situated at distal end of a thinlengthy probe and the necessity to control position of electronic beammake for design complexity of the device. At that, radiation energy isdetermined substantially by anode material. Impossibility of anodereplacement in the evacuated probe results in necessity of havingseparate device for each radiation energy desired. The same is true forchanging spatial radiation pattern by matching the radiotransparencyratio of different portions of the distal probe end. Operation of thedevice utilizing electronic beam is influenced with external magneticfields, thus necessitating to make arrangements on correspondingshielding. Realization of the probe as a part of X-ray tube complicatessubstantially its sterilization. Overcoming of this drawback byproviding the probe with removable sheath increases its diameter and isassociated with a rise in traumatism on utilization of the device.Therefore, primary field of utilization of said device is treatment oftumors of hollow organs requiring no puncturing and situated inimmediate communication with outer environment, such as urinary bladder,rectum, etc. Besides, said device, comprising probe as a constituentpart of X-ray tube, is applicable for treatment with X-ray radiationonly.

DISCLOSURE OF THE INVENTION

[0009] It is an object of the present invention to provide for technicalresult consisting in:

[0010] possibility of application for therapy utilizing not only X-ray,but other kinds of radiation as a flux of neutral particles as well;

[0011] design simplification and costs reduction due to avoidance ofutilization of vacuum and high voltage, and elimination of control meansof electronic beam and magnetic shielding;

[0012] easy transformation by the way of probe replacement, inparticular, for changes of its size, and changes in energy anddirectional radiation pattern acting on the pathological locus;

[0013] simplicity of the probe sterilization, and possibility ofutilization of interchangeable or disposable probes;

[0014] possibility of the probe disconnection from the rest of device,leaving it in patient's body, and utilization of the device at this timewith other probe.

[0015] In order to achieve mentioned kinds of technical result theproposed device for radiation therapy, similar to the known onementioned above, comprises probe device for introduction into patient'sbody and approaching of its distal end to pathological locus orimmediate introduction into it, irradiation source, and means offormation of particle beam of said radiation, oriented along thelongitudinal axis of said probe.

[0016] Distinction of the proposed device from the known one lies in thefact of said radiation source being the source of neutral particles inthe form of X-ray ones or gamma quanta or neutrons. At that, means offormation of particle beam of said radiation, oriented along thelongitudinal axis of the probe, is executed as collimator or lens,comprising aggregate of curved channels for radiation transmittance witha total internal reflection.

[0017] With such design of the proposed device, as distinct from theknown one, pathological locus is acted upon immediately with radiationof the neutral particles source used, coming through thin probe to thepathological locus or into it. Said radiation, notwithstanding the factof being created with a source situated outside of body of the illperson, doesn't affect healthy tissues on the way to the pathologicallocus. This is achieved due to its propagation inside of the probe.

[0018] Due to the absence of vacuum and high electric voltage in theprobe it may be executed as a removable one, thus making easy itssterilization. The device may be provided with a set of probes havingdifferent size.

[0019] The probe, except for its distal end or its separate portions,may be executed non-transparent for the particles emitted with radiationsource and intended for action on the pathological locus.

[0020] Means of the particle beam formation oriented along thelongitudinal axis of the probe may be situated both outside of theprobe—between it and the source of high energy neutral particles—andpartially or wholly inside of the probe.

[0021] In the case of the means of particle beam formation orientedalong the longitudinal axis of the probe situated wholly inside of theprobe and being a collimator, the latter may have single channel.

[0022] In the case of the means of particle beam formation orientedalong the longitudinal axis of the probe being executed in the form of alens comprising aggregate of curved channels for radiation transmittancewith a total internal reflection, such a lens may be, in particular, afocusing lens with a focus situated outside of the probe on continuationof its longitudinal axis. In this case, focus is located withinpatient's body near to or inside of the pathological locus.

[0023] Said lens may be also a lens for formation of quasi-parallel beampassing through the probe and going out from its distal end.

[0024] In the case of radiation source being an X-ray source, the lattermay be executed with a sectioned anode for on-line change in particleenergy.

[0025] A secondary target may be located at the distal end of the probe.In this case, source radiation dissipated by secondary target or excitedradiation of the secondary target material is used for radiationexposure.

[0026] In the case of the means of particle beam formation orientedalong the longitudinal axis of the probe being made in the form of lenscomprising aggregate of curved channels for radiation transmittance witha total internal reflection, such a lens may be, in particular, afocusing lens with a focus located on the secondary target.

[0027] In order to change characteristics of radiation dissipated andexcited in the secondary target material, distal end of the probe may bemade split with a possibility of replacement of the secondary targetmounted in it. At that, secondary target mounted in the distal end ofthe probe is one of the several in the device set supplied, for example,made of different metals.

[0028] For the on-line change of desired directional radiation patternemanating from the distal end of the probe and acting on thepathological locus, distal end of the probe may be made removable. Inthis case, probe has one of the several distal ends from the device set,executed with different transparency ratios of portions of the distalend surface of the probe for radiation dissipated and excited in thesecondary target material.

[0029] In order to ensure coagulation of wound channel arising in thecourse of puncture with a probe after completion of treatment procedure,the latter may be made electrically conductive and having on theoutside, except for the most remote portion of the distal end,insulating coating. In this case, the probe should have possibility ofbeing connected to electrocoagulator.

BRIEF DESCRIPTION OF DRAWINGS

[0030] The inventions proposed are illustrated with drawings, in whichare depicted:

[0031]FIG. 1—schematic representation of the device as a whole togetherwith several probes coming in the set;

[0032]FIG. 2—utilization of the device for irradiation of extendedtumor;

[0033]FIG. 3—utilization of the device with lens positioned outside ofthe probe for irradiation of a small tumor;

[0034]FIG. 4—lens positioning partially inside of the probe;

[0035]FIG. 5—device with a lens effecting collimation and focusing ofthe source radiation;

[0036]FIG. 6—the probe serving simultaneously as a collimator with asingle channel;

[0037]FIG. 7—utilization of the device in combination with coagulator;

[0038]FIG. 8—distal end of the probe with a secondary target installedin it, which is being irradiated with a quasi-parallel beam;

[0039]FIG. 9—distal end of the probe with a secondary target installedin it, which is being irradiated with a focused beam;

[0040]FIG. 10—a probe with several removable distal ends.

THE EMBODIMENTS OF THE INVENTION

[0041] The device proposed comprises (FIG. 1, A) a source of neutralparticles (X-ray or gamma quanta or neutrons), protective shield 2 witha diaphragm 3 situated in front of the outlet aperture of source 1,means 4 of formation of particle beam oriented along longitudinal axisof the probe 5. The latter has tapered distal end 7. Proximal end 6 ofthe probe 5 may be executed in such a way as to ensure possibility ofthe probe removal (for example, for sterilization and replacement withanother one). The set of the device may include several probes, forexample, of different length (FIGS. 1, B and C).

[0042] The probe may be similar in form and dimensions to a punctureneedle for biopsy.

[0043] In the course of device usage the probe is introduced, dependingon the localization of pathological locus, into one of the naturalpassages of patient's body or perform puncturing similar to biopsyprocedure.

[0044]FIG. 2 shows position of the probe 5 in the body of patient 11.Quasi-parallel beam 10 of radiation comes to the proximal end 6 of theprobe. This beam is transmitted through the inner channel of the probe 5and goes out through radiolucent distal end 7. The latter in the caseshown in FIG. 2 is situated in the immediate proximity of extended tumor12. The direction of the probe introduction is selected so that theradiation outgoing from the distal end 7 would enter the tumor 12 andpropagate in the direction of a larger dimension. The radiationpenetrating into the tumor affects directly tissues in median part ofthe tumor situated in its way. Tumor tissues surrounding the median onesare affected with the secondary radiation excited in the median tissues.Since radiation emerging from the distal end of the probe haspractically no effect on the healthy tissues, the intensity of primaryradiation of the source may be selected in such a way as to ensure thatthe intensity of secondary radiation of the median tissues reachingtumor periphery is on the level with that minimally sufficient fordamaging peripheral tissues. In this case, secondary radiation reachingbeyond tumor limits will not damage healthy tissues, which surround it.

[0045] To affect neoplasms having small size, it is expedient to use afocused beam outgoing from the distal end 7 of the probe 5. FIG. 3 showsembodiment of the device in which divergent radiation from X-ray sourcehaving small aperture 14 is focused with a X-ray lens 15 and transmittedthrough a probe 5 introduced into the body of patient to the center 16of tumor 13. Similar to the above considered case, peripheral tissues ofthe tumor 13 are irradiated with excited secondary emission.

[0046] When using a source of neutrons as radiation source, use of thedevice proposed may be combined with a method of boron capturing therapywhich ensures boron concentration in the tumor 5 (Advances in NeutronCapture Therapy. Editors: B. Larsson, J. Crawford, R. Weinrech.Elsevier, 1997 [5]).

[0047] Up-to-date technology of X-ray manufacturing allows to obtainsingle piece lenses of a small size (see, for example, M. A.Kumakhov. Ahistory of the X-Ray and neutron capillary optics. Optic of beams, p.p.3-17, Moscow, 1993 [6]), acceptable for placement partially or totallyinside of the probe. Corresponding embodiments of the device are shownin FIG. 4 and FIG. 5.

[0048] In FIG. 4, focusing lens 15 is situated inside of the probe 5,with divergent radiation from the source having small aperture 14 comingin at the input. Focusing is accomplished in the point 16 situatedoutside of the radiolucent distal end 7 of the probe 5 on thecontinuation of its longitudinal axis.

[0049] In FIG. 5, lens 18 is forming a beam focused in the point 16situated inside of the pathological locus 13, out of radiation of thesource 1 having relatively large outlet aperture 17. The upper part ofthe lens 18 has parallel channels and plays a role of collimator. Inthis part of the lens, quasi-parallel beam of the particles forms, whichid transmitted through its channels. After that, similar to ordinarylens for quasi-parallel radiation focusing, it is transformed intofocused beam coming out of the lower end of the lens 18. Protectiveshield 2 protects patient 11 against radiation of the source 1,scattering past the lens 18.

[0050] In all the cases considered the radiation used, though created bya source located outside of the patient's body, doesn't affect healthytissues situated on the way to the pathological locus. This is ensureddue to the fact of healthy tissues being mechanically isolated from theradiation beam path by the probe walls, as well as to their shieldingeffect. For that, they are made radio-opaque to the radiation used.Although oriented radiation beam directed into the probe may nottransverse walls of the probe, if being shaped sufficiently accurately,this measure is an additional guarantee of radiation being emitted onlythrough portions of the distal end of the probe intended for thispurpose.

[0051]FIG. 6 demonstrates utilization of the device, in which shaping ofthe close-to-parallel beam going out of the distal end 7 of the probe 5is effected by the probe itself. In the given case it functions as acollimator having single channel formed by side walls of the probe 5.With corresponding selection of the probe length and distance betweenits proximal end 6 and outlet aperture 14 of the radiation source,radiation 20 emerging from the distal end 7 has a small divergence angleand is close to parallel. Such work of the device is equivalent toplacing of the means of quasi-parallel particle beam shaping inside ofthe probe.

[0052] In order to effect radiation treatment, it is possible to usesimultaneously several probes introduced into different portions of atumor.

[0053] In all the cases of utilization of X-ray source as a radiationsource, the latter may be executed with a divided anode for on-linechanges in the particles energy.

[0054] In order to ensure coagulation of wound channel arising in thecourse of puncture with a probe after completion of treatment procedure,the latter may be made electrically conductive and having on the outside(see FIG. 7) an insulating coating 23, except for the most remoteportion 22 of the distal end. In this case, the probe should havepossibility of being connected to electrocoagulator 24. On applyingelectric voltage from the coagulator between the probe 5 and body ofpatient 11 in the course of probe removal (arrow 25 in FIG. 7),“welding” of the wound channel 26 takes place. It prevents spreading oftumor 13 cells beyond the malignant locus (in this case, technique usedis similar to that described in the patent of Russian Federation No.2120787 [7]).

[0055] A secondary target may be located in the distal end of the probe.In this case, source radiation dissipated with a secondary target orsecondary radiation of a target is used for radiation treatment.

[0056]FIG. 8 demonstrates a case of utilization of radiation 29 excitedin the secondary target material, which is brought out through windows28 transparent for this kind of radiation. Those latters are situated insuch a way as to form desired directional pattern of emergent radiation.For example, in case of uniform distribution of windows in a narrowstrip over perimeter of the distal end 7, radiation will be concentratedin a narrow spherical sector. By changing depth of the probeintroduction into the body of patient (in particular, into the tumor),position of this sector may be regulated for treatment of the selectedpart of the tumor. At that, different treatment tactics may be realized.For example, the probe may be displaced at variable speed or brought tostop for different time periods in different locations, thus regulatingthe degree of radiation exposure of different parts of the tumor,depending on its size in the direction perpendicular to longitudinalaxis of the probe.

[0057]FIG. 9 demonstrates utilization of radiation dissipated by thesecondary target 27. Due to isotropic nature of the latter, by makingthe distal end 7 of the probe radiolucent and target locating close tothe most remote part of the distal end, may be obtained nearlyomnidirectional radiation 29, including spreading partially backwards(upward in FIG. 9). Introduction of the distal end 7 directly into thetumor ensures irradiation of the largest part of tumor tissuessurrounding this end.

[0058] By utilizing secondary targets, the advantages of the deviceproposed, which requires no evacuation of the probe, are realized to astill greater extent. The replacement is made possible not only of theprobe as a whole, but also of its distal end 7, for changeover from onetype of the secondary target used to the another one. FIG. 10demonstrates realization of the probe 5 with a removable distal end 7and embodiments of the distal end with two discussed above types of thesecondary targets 27 and formation of two kinds of directional patternsof secondary radiation 28, 29 (see FIGS. 10, A, B, and C,correspondingly).

[0059] In order to change characteristics of dissipated and secondaryradiation, distal end of the probe may be made split with a possibilityof replacement of the target mounted in it. At that, secondary targetmounted in the distal end of the probe is one of the several in thedevice set supplied, for example, made of different metals.

[0060] The probe 5 may have one of the several distal ends in the deviceset executed with different transparency ratios of surface portions ofthe distal end of the probe for radiation dissipated and excited in thesecondary target material.

Industrial Applicability

[0061] The device proposed may be realized by utilization both typicalindustrially manufactured radiation sources, such as X-ray tubes, andsources of neutron radiation and radioisotopes.

Sources of Information

[0062] 1. Aspects of Clinical Dosimetry, Ed. R. V.Stavitskij, Moscow,“MNPI”, 2000 (in Russian).

[0063] 2. Radiation Therapy of Malignant Tumors. Guide for Physicians.Ed. Prof. E. S.Kiseleva, Moscow, “Meditsina” Publishing House, 1996 (inRussian).

[0064] 3. M. A.Kumakhov. X-ray means of location determination andradiation therapy of malignant neoplasms. International applicationPCT/RU 00/00273, international publication WO 01/29845A1, Apr. 26. 2001.

[0065] 4. Nomikos et al. Miniaturized low power X-ray source. U.S. Pat.No. 5,153,900, publ. Oct. 06, 1992.

[0066] 5. Advances in Neutron Capture Therapy. Editors: B.Larsson,J.Crawford, and R.Weinrech. Elsevier, 1997.

[0067] 6. M. A.Kumakhov. A history of the X-Ray and neutron capillaryoptics. Optic of beams, p.p. 3-17, Moscow, 1993.

[0068] 7. S. A.Astrakhantsev et al., Needle device for biopsy andcoagulation. Patent of Russian Federation No.2120787, publ. Oct. 27.1998.

1. Device for radiation therapy comprising hollow probe (5) forintroduction into the body of patient and approaching of its distal end(7) to pathological locus or introduction directly into it, source (1)of radiation, and means (4) of shaping the particle beam of saidradiation oriented by the longitudinal axis of the probe, characterizedin that the said source (1) of radiation is a source of neutralparticles in the form of X-ray or gamma quanta or neutrons, and means(4) of shaping the particle beam oriented by the longitudinal axis ofthe probe is executed in the form of collimator or lens comprisingaggregate of curved channels for radiation transmission with a totalinternal reflection.
 2. Device according to claim 1, characterized inthat the probe (5) is made removable.
 3. Device according to claim 2,characterized in that it has installed one of the several probes fromthe device set having different length.
 4. Device according to claim 1,characterized in that the means (4) of shaping particle beam oriented bylongitudinal axis of the probe is situated partially or wholly withinthe probe (5).
 5. Device according to claim 4, characterized in that theprobe (5) is made removable.
 6. Device according to claim 5,characterized in that it has installed one of the several probes fromthe device set having different length.
 7. Device according to claim 4,characterized in that the probe (5), except for the distal end (7) orits separate portions, is made non-transparent for particles of theradiation used.
 8. Device according to claim 7, characterized in thatthe probe (5) is made removable.
 9. Device according to claim 8,characterized in that it has installed one of the several probes fromthe device set having different length.
 10. Device according to claim 1,characterized in that the probe (5) is made electrically conductive withpossibility of its connection to electrocoagulator (24) and having onthe outside insulating coating (23), except for the most remote part(22) of the distal end (7).
 11. Device according to claim 10,characterized in that the probe (5) is made removable.
 12. Deviceaccording to claim 11, characterized in that it has installed one of theseveral probes from the device set having different length.
 13. Deviceaccording to claim 1, characterized in that the probe (5), except forthe distal end (7) or its separate portions, is made non-transparent forparticles of the radiation used.
 14. Device according to claim 13,characterized in that the probe (5) is made removable.
 15. Deviceaccording to claim 1, characterized in that it has installed one of theseveral probes from the device set having different length.
 16. Deviceaccording to claim 13, characterized in that the probe (5) is madeelectrically conductive with possibility of its connection toelectrocoagulator (24) and having on the outside insulating coating(23), except for the most remote part (22) of the distal end.
 17. Deviceaccording to claim 16, characterized in that the probe (5) is maderemovable.
 18. Device according to claim 1, characterized in that it hasinstalled one of the several probes from the device set having differentlength.
 19. Device according to claim 1, characterized in that the probe(5) is made electrically conductive with possibility of its connectionto electrocoagulator (24) and having on the outside insulating coating(23), except for the most remote part (22) of the distal end (7). 20.Device according to claim 19, characterized in that the probe (5) ismade removable.
 21. Device according to claim 20, characterized in thatit has installed one of the several probes from the device set havingdifferent length.
 22. Device according to any of the claims 1 to 21,characterized in that the means of shaping the particle beam oriented bylongitudinal axis of the probe, made in the form of lens comprisingaggregate of curved channels for radiation transmission with totalinternal reflection, is a focusing lens (15) with a focus (16) locatedoutside of the probe (5) on continuation of its longitudinal axis. 23.Device according to claim 22, characterized in that it comprise X-raysource as radiation source (1).
 24. Device according to claim 23,characterized in that the X-ray source is made with a divided anode. 25.Device according to any of the claims 1 to 21, characterized in that themeans (4) of shaping particle beam oriented by longitudinal axis of theprobe, totally located inside of the probe, is a collimator havingsingle channel.
 26. Device according to claim 25, characterized in thatit comprise X-ray source as radiation source (1).
 27. Device accordingto claim 26, characterized in that the X-ray source is made with adivided anode.
 28. Device according to claim 26 or claim 27,characterized in that it has secondary target (27) located in the distalend (7) of the probe (5).
 29. Device according to claim 28,characterized in that the distal end (7) of the probe (5) is maderemovable.
 30. Device according to any of the claims 1 to 21,characterized in that the means (4) of shaping the particle beamoriented by longitudinal axis of the probe, made in the form of lenscomprising aggregate of curved channels for radiation transmission withtotal internal reflection, is a lens (15) forming quasi-parallel beam(10).
 31. Device according to claim 30, characterized in that itcomprise X-ray source as radiation source (1).
 32. Device according toclaim 31, characterized in that the X-ray source is made with a dividedanode.
 33. Device according to claim 31 or claim 32, characterized inthat it has secondary target (27) located in the distal end (7) of theprobe (5).
 34. Device according to claim 33, characterized in that thedistal end (7) of the probe (5) is made removable.
 35. Device accordingto claim 29 or claim 34, characterized in that the probe (5) has one ofthe several distal ends (7) in the device set, executed with differenttransparency ratios of surface portions of distal end of the probe forradiation dissipated and excited in the secondary target (27) material.36. Device according to any of claims 1 to 21, characterized in that ithas X-ray source as radiation source (1).
 37. Device according to claim36, characterized in that it has secondary target (27) located in thedistal end (7) of the probe (5).
 38. Device according to claim 37,characterized in that the means of shaping the particle beam oriented bylongitudinal axis of the probe, made in the form of lens comprisingaggregate of curved channels for radiation transmission with totalinternal reflection, is a focusing lens (15) with a focus located on thesecondary target (27).
 39. Device according to claim 36, characterizedin that the X-ray source is made with a divided anode.
 40. Deviceaccording to claim 39, characterized in that it has secondary target(27) located in the distal end (7) of the probe (5).
 41. Deviceaccording to claim 39, characterized in that the means of shaping theparticle beam oriented by longitudinal axis of the probe, made in theform of lens comprising aggregate of curved channels for radiationtransmission with total internal reflection, is a focusing lens (15)with a focus situated on the secondary target (27).
 42. Device accordingto any of the claims 37 to 41, characterized in that the distal end (7)of the probe (5) is made removable.
 43. Device according to claim 42,characterized in that the probe (5) has one of the several distal ends(7) in the device set, executed with different transparency ratios ofsurface portions of distal end of the probe for radiation dissipated andexcited in the secondary target (27) material.